Is there one common subscription to use Merlin Project on Mac, iPhone and iPad?

No. We do not offer subscriptions to different Merlin products in a bundle.

Not every customer needs all versions of our software, therefore we have decided not to combine different product versions to one subscription.

Merlin Project for Mac, iPhone and iPad as well as Merlin Project Express are individual products for different operating systems (macOS and iOS) and scopes. They require individual subscriptions sold separtely.

Questions regarding subscriptions in the App Store, are directly answered by Apple on their help pages.